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mcx_hartmann.pdf | 2006-03-09 05:29:41 | Sheung-W Ng |

## Hartmann Flow Physics at Plasma-Insulator Boundary in the Maryland Centifugal Experiment (MCX)

Author: Sheung-W Ng

Submitted: 2005-12-21 23:40:44

Co-authors: A.B.Hassan

Contact Info:

IREAP, University of Maryland, College Park

Dept of Physics, 127, Universi

College Park, MD 20742

USA

Abstract Text:

Hartmann flow is the flow of magnetized fluid past a bounding surface [1]. If the plasma is forced to flow in a channel with the magnetic field connects the two channel plates, and if the plasma is assumed to have no-slip boundary conditions at the plates, the solution for the plasma flow is almost rigid, frozen-in flow in most of the plasma but with a sharp boundary layer near the wall. The scale of the layer is the macroscopic scale divided by the Hartmann number, $H_a =B a/(eta mu c^2)^(1/2)$, where $H_a$ is very large for fusion grade plasmas. The boundary layer violates frozen in (hence the resisitivity) and this leads to a large friction. The resulting confinement time of the momentum is almost of order Alfvenic x $(n M eta c^2/mu)^(1/2)$. This time is much shorter than the crossfield viscosity time, thus making along the field coupling stronger in a rotating magnetized plasma. This flow is very relevant to the MCX plasma [2]. The field lines are open and end on an insulator with plasma flowing across. The MCX system is more complicated, with ionization, recombination, neutral-ion charge exchange, collisionless effects, etc. In previous work, we have solved for the neutral and plasma profiles with ionization and charge-exchange near the insulator. We are now extending this work to include flows, thus Hartmann flows with neutral effects. First findings on this problem will be presented. Because the plasma density is very small at the insulator and the neutral density is high, the Hartmann layer physics changes. In particular, the enhancement of resisitivity from electron-neutral collisions and collisionless long mean free path physics need to be included. Centrifugal confinement will make these effects even more pronounced. Understanding of this interaction is crucial in assessing the scaling up of MCX to fusion device parameters.

Work supported by DOE

[1] J. D. Jackson, "Classical Electrodynamics", 2nd ed. (Wiley, New York, 1975).

[2] Y. M. Huang, Ph. D. thesis, University of Maryland, College Park, 2004.

Characterization: A5

Comments:

The author would like to have this poster placed along with other MCX posters. Thank you very much.